Radio altimeter and panoramic reception system



Dec. 19, 1950 M. WALLACE 2,534,839

RADIO ALTIMETER AND PANORAMIC RECEPTION SYSTEM original Filed se'pt. 21, 1940' 9 sheets-sheet 1 Erica- E Dec. 19, 1950 M. WALLACE 2,534,839

RADIO ALTIMETER AND PANORAMIC RECEPTION SYSTEM original Filed sept. 21. 1940 9 sheets-sheet 2 M. WALLACE 2,534,839 RADIO ALTIMETER AND PANORAMIC RECEPTION SYSTEM Dec. 1'9, 1950 9 Sheets-Sheet 3 Original Filed Sept. 21, 1940 Dec. 19, 1950 Y M. WALLACE RADIO ALTIMETER PANORAMIC RECEPTION SYSTEM original 'filed sept. 21, 1940 9 Sheets-Sheet 4 d@ JQ Dec. 19, 1950 M. WALLACE 2.534.839

RADIO ALTIMETER AND PANORAMIC RECEPTION SYSTEM Original Filled Sept. 21, 1940 9 Shegts-Sheet 5 .n----ulll I-- I-- Dec. 19, 1950 M. WALLACE 2,534,839

RADIO ALTIMETER PANORAMIC RECEPTION SYSTEM Original Filed Sept. 21, 1940 9 Sheets-Sheet 6 SQ (/AR WA YE Dec. 19, 1950 M. WALLACE 2,534,839

RADIO ALTIMETR AND PANORAMIC-RECEPTION SYSTEM Original Filed Sept. 2l, 1940 9 Sheets-Sheet 8 TIE- E E a 45 31E- E E b 1NVENT0R.` @ina-fc4@ Maffaca M. WALLACE Dec. 19, 195o RADIO ALTIMETER AND PANORAMIC RECEPTION SYSTEM 9 Sheets-Sheet 9 Original Filed Sept. 2-1

MMIMEII INVENTOR GE w 52: ...Eo

`latenteci Dec. 19, 195i) UNITED STATES PTENT OFFICE RADIO ALTIMETER AND; PANORAMIC RECEPTION SYSTEM Marcel Wallace, New York, N. Y., assignor, by mesne assignments, of one-half to Panoramic Radio Corporation, New York, N. Y., a corporation of New York 25 Claims.

My invention relates` broadly to systems of radio navigation and more particularly to im proved methods and circuit arrangements for radio beacons and panoramic reception for use in navigation of mobile bodies.

This application is a division of my copending application Serial No. 357,814, filed September 21, 1940, for Radio Altimeter and Panoramic Reception System, now Patent No. 2,378,604, issued June 19, 1945.

Inv my Patents No. 2,279,151, granted April 7, 19,42, for Panoramic Radio Receiving System, and No. 2,273,914, granted February 24, 1942, for Radio Navigation System, I have shown that by means of a frequency scanning panoramic receiver installed on board an airplane, it is possible to observe one or a plurality of signals which are radiated from transmitting stations located at danger points, such as mountain peaks, for Warning the pilot of the approach of the plane to terrain which may be hazardous to aerial navigation.

One of the objects of my invention is to provide a system for emitting a signal of such a nature as to inform those who receive it of the altitude of a fixed or mobile body equipped with the apparatus of my invention.

A further object of my invention is to provide an arrangement of a signal generator which can be synchronized with a receiver on board a mobile body, in such a manner that the signal supplied by the generator does not interfere with the reception of another signal at the same frequency originating from another body.

Another object of my invention is to provide simple apparatus for the reception and convenient interpretation of a plurality of signal` indica.- tions, and information which can be received visually, or both visually and aurally.

A further object of my invention is to provide simple transmitting and receiving apparatus for providing navigational information without moving parts and with all the circuits electronically controlled.

A still further object of my invention is to provide a simple system for distinguishing between signals of a given system and others of another system although such beacons may use the same portion of the frequency spectrum, by changing the rate of frequency change from one system to the other. This is rendered possible by the use of panoramic receivers having means for varying at will their rate of frequency sweep, so as to make it correspond to the rate of frequency variation, or of a harmonic thereof, of a signal. This feature permits the elimination of sources of periodic noises such as produced by vibrators, motors, etc.

Another object of my invention is to provide means for trai-lic control at airports, and therefore permit handling of large numbers of aircraft during conditions of poor visibility.

Still another object of my invention is to provide an absolute altimeter control requiring no adjustments, along airways and airports.

Another object of my invention is to combine such altitude indications and trafic controlling system, with means for communication to selected stations.

Still another object of my invention is to provide means for signalling from the ground to particular aircraft selected according to their altitude.

Still another object of my invention is to provide means for signalling from the ground to particular aircraft selected according to their altitude.

Still another object of my invention is to permit aircraft to fly in` different directions along such airways and maintain a certain minimum and maximum vertical separation between them.

vAnother object of my invention is to simplify methods ci instrument landing by using the absolute altitude as indicated from the airport, as a vertical indication and to combine such indications with those of distance and direction.

Another object of my invention is to provide means for aircraft identification either from aircraft to aircraft or from ground to aircraft,

Other and further objects of my invention will be apparent from the specifications hereinafter following by reference to the accompanying drawings, in which:

Figure 1 is the diagram of an aneroid cell controlled transmitter used in my invention; Fig. la is a block diagram showing the relationships between an aneroid cell, a transmitter and a receiver according to my invention; Fig. 2 is another block diagram showing in a more detailed form the principal parts and their relationship in a fully electronically controlled frequency scanning panoramic receiver, and of an aneroid cell controlled transmitter, said receiver automatically keying oif the transmitter so as to -prevent interference between the two; Fig. 3 represents a series of curves showing the frequency Versus gain and power relationships between the various elements shown in Figs. 2 and 4; Fig. 3a represents a series of curves showing the phase relationship between the sawtooth voltage controlling the periodic response of an aural device and the periodic keying of a transmitter as shown in Fig. 4a; Fig. 4 is a detailed diagram of a receiver such as represented in Fig. 2; Fig. 4a is a similar receiver combining electronic and mechanical means; Fig. 5 is a block diagram of another electronically controlled receiver and transmitter similar in function to those shown in Fig. 2, with the difference that the said receiver is simultaneously indicating signals present over distinct portions of the frequency spectrum; Fig. if

6 shows details of the special elements used in connection with the apparatus shown in Fig. 5; Fig. 7 shows a series of curves explaining the time and voltage relationship of various elements of Fig. 5; JFig. Y8 is a special dynamically balanced condenser combined with a synchronous commutator; Fig. 9 is a diagram of an apparatus in which the device of Fig. 8 is used; Fig. 10'shows a commutator and its connections for obtaining a square wave current; Fig. 11 is a schematic dia- 'f gram showing a mechanically controlled frequency scanning panoramic receiver simultaneously indicating two bands of the frequency spectrum and using the devices shown on Figs. 8 and 10; Fig. l2 is a 'diagram explaining the phase relationship between elements of Fig. 11; Fig. 13 is a schematic diagram representing part of a panoramic receiver using an electronic source of sweep voltage, a mechanical commutator and a periodically tunable condenser. It also shows the t method of synchronizing these elements; Fig. 14 represents a block diagram of the principles used in a dual-frequency beacon according to my invention, in which two transmitters are continuously operated; Fig. 15 represents a screen of an aircraft type receiver embodying the features of my invention; Fig, 16 represents the screen of a similar ground type receiver; Fig. 17 represents the phase relationship between a sine wave used for cathode ray sweep and transmitter modulation, and a pyramid wave for frequency sweep; Fig. 18 shows a vertically defined airway, with vertical separation for aircraft traveling in opposite directions; Fig. 19 is a block diagram of a simplified transmitter in which two oscillatortransmitters are alternately operated; Fig. 2O shows a series of vertical level markers leading planes to a landing runway from a vertically defined airway; Fig. 21 shows the appearance of the screen and dial arrangement of a dual band frequency scanning panoramic receiver, showing simultaneously a plurality of beacons, their geographic position and also a plurality of obstacles and their respective altitudes with respect to the observer; Fig. 22 is a reversible transmission pattern of a dual-frequency beacon creating an equisignal path; Figures 22a and 22h show how certain signals transmitted from a transmission pattern such as shown in Figure 22 appear on a frequency scanning panoramic receiver; Figure 23 is a diagram of a wind controlled directive beacon; Figure 24 is a plan view illustrating a landing system in accordance with the present invention, and the radiant energy patterns provided thereby; and Figure 25 is a View in side elevation of the system of Figure 24, showing the relations vertically and in range of the beacon patterns provided by the system of Figure 24.

In the carrying out of my invention, advantage is taken of the properties of a frequency scanning panoramic receiver, such as described in my patents, supra.

In the system of my invention, I provide means capable of z 1. Continuously observing the variations of signal strength of two or more signals.

2. Observing the variations of frequency of two or more signals.

3. Determining the frequency of modulation of lany signal, by synchronizing the band sweep frequency with the modulation of the transmitter.

Considering the large number of special terms required in connection with the technique of frequency scanning panoramic reception, and in order to avoid repetition of explanation, or misinterpretation of these terms, I shall refer in the description which follows to standardized terms whose definitions are given herein below:

A panoramic receiver is a radio receiver having means for reproducing on a cathode ray screen substantially'simultaneously in the form of individual signs, the frequency and amplitude characteristics of a plurality of independent signals distributed over a given portion of the radio frequency spectrum. When therpresentation is produced by frequency scanning, Yor periodic tuning of the radio receiver, the receiver is known as a frequency scanning panoramic receiver.

By signal strength (s) is meant the input strength of a signal measured in microvolts at the antenna terminals.

The frequency sweep axis is the line traced on the screen of the cathode ray tube. Its point of origin corresponds to the point on that line where the luminous spot stops, when the sweep voltage applied to the deilecting elements passes through Zero value.

The amplitude axis is the imaginary line normal to the frequency sweep axis and meeting it at the point of origin.

Frequency sweep rate is the number of times the frequency scanning panoramic receiver is periodically tuned during an interval of one second.

The deflection amplitude (u) is the linear deflection produced by a signal, measured on the amplitude axis.

Amplitude discrimination, for a given gain control setting, is the ratio dv/ds between the increase of deflection amplitude (dv) and the increase of signal strength producing it (ds). It is a linear amplitude discrimination when the amplitude discrimination remains constant for any value of signal strength dtv ds :s

It is a non-leaner amplitude discrimination when the amplitude discrimination varies with variations of signal strength,

The logarithmic amplitude discrimination is a non-linear amplitude discrimination in which f(s) is a logarithmic function.

The Visual frequency range is represented by the minimum frequency Fm and maximum frequency FM corresponding to the extremities of the frequency sweep axis.

'I'he frequency sweep is the difference between FM and Fm and represents the bandwidth visually covered.

The frequency spacing is the band width represented in kilocycles, covered over one linear unit along the frequency sweep axis. It is expressed, for example, in kilocycles per mm.

The Orig-in frequency is the frequency at which the receiver is tuned at the point of origin on the frequency sweep axis.

The center frequency is that frequency which is substantially equally separated from FM and Fm and is, therefore. ,in the center of the Visual frequency range.

Tuning a panoramic receiver, is the action of displacing the origin or center frequency along the frequency Spectrum.

Tuning range is represented by the minimum and maximum frequencies receivable (in kilocycles) by tuning the panoramic receiver from one end of a band to the other, (Fmm and Fmex).

. Frequency range is the number of kilocycles resulting from the difference between Fmax and Fmin.

Bias tuning is the panoramic tuning obtained through the variation of biasing voltage on the reactor tube.

In order to explain the operation of my invention I must first refer to some well known principles involving the generation of a signal who-se frequency is characteristic of the altitude or of the local pressure. A portion of the frequency spectrum may be assigned for the purpose of these indications, and may be subdivided according to a predetermined relationship between frequency and altitude. This relationship may be linear. For example, if for altitude zero, (corresponding to sea level) the frequency Fmin is assigned and for an altitude of H feet, a frequency Fmax is allotted, any intermediary altitude, for example h, can conveniently correspond to a frequency This term will becalled in the future: the altitude frequency corresponding to altitude h.

Instead of this simple linear frequency versus altitude distribution, other functions may be determined, which instead of being linear, can be, for example, exponential, the frequency varying proportionally to the percentage of altitude variation, etc. An element such as an altitude or pressure operated instrument is employed for controlling the frequency determining circuit of the signal generator.

Such a generator is shown in Fig. l, in which an aneroid cell i, supported by block 4, is made to Vary the distance between condenser plates 2` and 3. The capacity of the condenser 2--3 varies according to the local pressure as impressed upon the aneroid cell, This condenser operates to tune a circuit including an inductance 5 and the whole tuned circuit determines the frequency of oscillation of a tube 6. This is a simple type of local pressure of altitude indicating oscillator, which is employed in several arrangements of my invention described hereinafter.

The readings of the frequency indications of several such oscillators, may be made with a panoramic receiver, or by a frequency scanning panoramic receiver such as described in my pattents, supra. The frequency sweep axis on the cathode ray tube can be calibrated in altitude, and from the position of each deflection, the altitude of each obstacle can be read.

When such an altitude indicating signal generator is mounted on board aircraft and if this air-craft carries on board a panoramic receiver which in the altitude band of the frequency spectrum, the locally generated signal covers that part of the spectrum which corresponds to its own altitude frequency. If another aircraft equipped with an identical altitude indicating signal generator is in the proximity of the rst, and at the same altitude, the observer may not be able, therefore, to distinguish its signal, on account of said local signal which interferes With the other signal presumably weaker.

My present invention removes this difficulty. In order to do this, I provide a combination between the local signal generator and the panoramic receiver, in such a manner that the output power of the first is controlled in synchronisrn with the periodic tuning of the other. By means of a synchronous switch, which can be either electronic (Figs. 2, 3, 4) or mechanical (Figs. V3d, llai) the transmitter is shut off entirely, or only reduced in power, periodically, every time the receiver tunes through, or must indicate a frequency close to that of the local transmitter.

Such a combination is represented as a block diagram in Fig. 1a.

I call such a combination between a panoramic receiver and aneroid cell controlled transmitter, which eperate in synchronism with one another a stratoscope a yword which will be used from time to time to denne this instrument.

en electronically controlled stratoscope is shown in Fig. 2 in the form of a block diagram for explaining my invention. The frequency scanning panoramic receiver illustrated consists of a signal input circuit A, an oscillator B, a converter C and two channels of intermediate frequency amplifiers D and E, The oscillator is periodically tuned over a band of frequencies by a Variable reactance tube F which, in turn, is controlled by a sweep voltage generator G. This generator produces the source of sweep voltage applied to one set of deflecting plates of the cathode ray tube H. The intermediate frequency channel D is sharply tuned and the signals passing through it are detected and applied to the other set of dede-:ting plates of the cathode ray tube.

The parallel channel E is broadly tuned or tuned slightly olf the frequency of channel D and develops at its peak a much weaker signal than channel D. However, over certain portions of the frequency spectrum, immediately adjacent to the band pass characteristics of the channel D, it develops a stronger signal.

This is illustrated in Fig. 3, in which the abscissa represents the frequency variation (or time variation, the two being linked together) and the ordinate represents gain of channels D and E o-r power developed by oscillator transmitter J.

Supposing that the oscillator transmitter J emits a signal on frequency Fh and the frequency scanning panoramic receiver starts tuning from a frequency Fmin toward a frequency F er. As it approaches frequency Fh it passes through a region F1 F2 when the I. F. channel E develops an impulse which is applied at once to a keying tube lwhioh triggers on" the transmitter J (see curve J on Fig. 3), before or almost at the time when the channel D could start building up a from the transmitter. The time constants of the trigger circuit are such as to maintain the transmitter keyed off during the predetermined time interval, equivalent to a variation of frequency of from Fa to F4. When the oscillator starts again, its frequency is out of the tuning range of the receiver, so that the latter is unaffected by the presence of that local signal. The signals picked up by the channel D are detected, amplified and applied to the other set of de; fleeting plates of the cathode ray tube H. These signals will be always synchronized with the sweep ass/1,839

appliedV to the first set of deflecting plates, so that each deflection will appear stationary, in a positionl determined by the frequency of the signal and of an amplitude determined by the signal strength.

In parallel with the cathode ray tube, preferably through a proper coupling device, it is possible to feed an audible device such as a loudspeaker or head-phones, or a special visual device such as a neon bulb, etc. trated in Fig. 4a, as 34a and 34h. This is important in case of collision warnings. YThe speed of the planes being great, it is possible that the pilot may not be aware of the appearance of a Visual danger signal on the screen, but his attention would be drawn at once if this signal will produce a distinctive noise in the loud-speaker or a light on the panel, which is exactly what happens. This is a very important feature of my invention, which adds to the safety of the flier.

In the circuit diagram of Fig. 4, the input circuit A is constituted by a receiving antenna 8, an inductance tuned by condenser S and an amplifier tube i2. The frequency modulated oscillator B is constituted by the triode i4 :and a circuit tuned by condenser i i. Directly connected to the tuned circuit of this oscillator, I show the frequency modulating channel F constituted by a thermionic tube l5 which acts as a reactance in parallel with said tuned circuit. By properly adjusting the phase relationship b-etween the input and output circuits of tube i5, as determined by capacities, resistors and choke (4E), Iii, 132) the reactance of this tube will increase or decrease the frequency of the oscillator lll by an amount depending on the voltage impressed on the grid 43 of the tube i5 in a direction depending on its polarity.

An alternating voltage, preferably produced by a sawtooth oscillator i5 and amplified by tube il' (corresponding to G in the block diagram) is fed to the variable reactance tube l5, through apotentiometer 26 and a voltage balancing potentiometer 'iii which is shunted by a battery 'il The adjustment of potentiometer EEB controls the biasing voltage on the grid 43, consequently the average reactance value of the tube i5. It determines, therefore, the average frequency at which the receiver will operate when an alternating voltage is fed on the grid i3. The potentiometer 2S controls the amplitude of this voltage, which in turn controls the reactance variation of tube i 5, and therefore, the bandwidth of oscillator iLi. The frequency of the sweep voltage can be adjusted by means of a multi-position selector switch 23 and the plate voltage controlling rheostat 8i. This frequency can be tied up or synchronized to any desired periodic voltage source, such as power supply, etc.

The converter corresponding to C is tube i3 whose grid t@ is coupled to the input amplifier tube l2 and frequency modulated oscillator it. The converted signal is developed in the I. F.

transformer 55 having two secondaries shown at 36 and 3l. The secondary 3e is tuned to the same frequency as the primary of transformer d5 and feeds the high gain, sharply tuned channel corresponding to D, composed of two amplifying stages comprising the tubes i8 and i9 and transformers it and il.

The signals are then detected and reamplified by means of a combined diode-triode thermionic tube 253. One diode plate 48 applies the rectified signal to a resistor 54 and the voltage drop Such devices are illus-I CIR through it is used to automatically control the gain of the amplifying tubes I8 and I9 by applying appropriate voltages at their grids through resistors 5@ and 5I, which are by-passed with condensers 52 and 53. The action of this automatic volume control is very important in the operation of the system of my invention because it will prevent Va signal from building up in amplitude beyond a given point, and instead, will compress the other signals weaker than it, so as to maintain their amplitudes as indications of their field strength. It will also tend to equalize rapid variations of deflection amplitudes due to variations of signal strength caused by reflections.

rl`he time constant of the circuits must be longer than the time period in which the receiver is tuned from minimum to maximum so that a signal impulse received in one tuning cycle will exert its volume control action in the next tuning cycle or cycles. Its action may be amplified if desired and this action actually determines the deflection amplitude of the receiver and its amplitude discrimination. Without this A. V. C. this amplitude discrimination is linear and with A. V. C. it is logarithmic. It is therefore possible to determine the ratio between various signal strengths by the difference between their corresponding deflections.

rlhe other diode plate 49 is connected to the diode i8 by means of a condenser 55 and develops a rectified pulsating current which is applied to an amplitude controlling potentiometer 30 and from there through a condenser 56 to the -grid of the triode section of the tube, which acts as a low frequency amplifier of the pulsating current.

A potentiometer 3| is provided for the important function of thresholding the signals. This operates as follows: The diode plate 49 of the diode-triode tube 2E! is returned to the power supply circuit by means of resistors 12 and 'E3 to this potentiometer 3l a, leg of which is at ground potential. The anode potential is taken from the cathode ray elements power supply 'Effi which is dropped to ground potential through a series of resistors including l5, iii, 'il and 78, some of which act as focus and intensity controls for said cathode ray tube.

By being able to make the diode plate 49 of any potential desired from zero up to a few hundred volts negative, it is possible to out out or prevent detection of any signal which does not exceed a desired value. This control acts, consequently, as an adjustable threshold devi-ce, which is useful for eliminating either noises which are below the signal levels or weak signals which are not interesting to the observer and which may confuse him. This threshold potentiometer can be calibrated in field strength, whether micro-volts or decibels for measuring the field strength of any signal. It is therefore useful also for measuring the difference between deflection amplitudes, which as said above, corresponds to ratio between signal strengths.

rf he potentiometer 3B which controls the amplitude of the signals applied to the output device, will cut all deflections in such a manner as to reduce them all in the same proportion. Therefore, the deflection ratios remain constant. By using, however, the threshold control we change the ratio between the deflection amplitudes and this become useful when we want to exaggerate or emphasize the difference of two deflections nearly equal in amplitude, as is necessary in the dual-frequency beacons described hereinafter.

The. pulses resulting from the reception of a series of stations are of extremely short duration, this depending upon the frequency of the sweep-voltage, the bandwidth and selectivity of theV I. E'. stages. This means that the amplier must have certain frequency characteristics which permit the amplification of frequencies of Ythe order of a few thousand cycles per second. These frequency characteristics are determined by the values of the grid, plate and cathode resisters El, 58, 60. A resistor 59 connected to the high voltagesource maintains the exact bias required under conditions of varying load. The amplified pulses are applied through a condenser l to one deflecting plate 62 of the -cathode ray tube 23, but it can also be connected by means of a switch 35 to an auditive output stage of device 34 for the audible or additional visual warning.' The perpendicular deecting plate 53 of the cathode ray tube is connected t the sweep voltage rgenerator i after amplifying its output vthrough tube Il. The frequency of this sweep should be sufficiently high to produce a rapid sweep of the cathode ray beam, which `should appear substantially flickerless on the fluorescent screen of the cathode ray tube.

The secondary 3l of I. F. transformer 45 feeds the transformer 54 which is connected to a diode detector and amplifier itube 2l which correspondsV .to the amplifying channel E of Fig. 2. A very strong signal produces across the condenser 65 and resistor 56 a substantial negative voltage .which is applied to the grid t8 of a keying or .trigger tube 22 `(corresponding to I). The plate .of this tube is connected to the cathode of the transmitter oscillator tube 6 whose frequency is controlled, as explained hereinbefore, by the `variations of pressure as impressed upon aneroid cell I.

rlhe tube 22 `offers the proper amount of resistance in the cathode lead of the oscillator 6 when no signal is applied to the grid 3, which is returned to ground by the grid resistor 61.

The signal, however. builds up on the condenser 69 and grid 68 a negative voltage which triggersoif `the plate current of tube E which stays shut off until the charge of condenser 59 leaks out through resistors 66 and 61.

The time constants of this circuit can. be adjusted to keep the transmitter turned oi just the length of time desired, as explained hereinafter.

The voltage developed by the tube 2l is low ,even when signals originating at a certain distan-ce are present, but is great in the presence of the local signal, which `builds up to several hundred thousand micro-volts in that stage, be-

fore the sharply tuned stages i8, I9 have time to build a substantial signal. A variable coupling between the primary and secondary of transformer 64. permits the proper adjustment of the cut-oil of the local transmitter. The tuning of this primary and secondary is such as to make it act as a filter of broad band pass characteristics.

All the potentials required for the frequency scanning panoramic receiver are produced by a common source of power supply and all can have common ground return to the chassis.

The frequency scanning panoramic receiver described herein can be made to cover a rather substantial hand by ganging the condensers s, le, H, or by vusing band filters. The bandwidth of the receiver .will be determined bythe voltage variations applied tothe grid 43 of tube i5, which is controlled by the potentiometer 26. The latter acts, therefore, as a band expansion or band compression device. If the constants of the circuit of tube i5 are properly adjusted, it is possible to make the frequency shift of the oscillator I4 substantially equal both above and below its average frequency, which permits a panoramic observation of equal bands immediately above or below a given center frequency. If the total band width is not too great, the input stages l2, I3, may be made of sufficiently broad band pass characteristics to avoid the necessity of tuning the condensers 9 and I0 and still obtain substantial linearity of response over the desired band, as illustrated in Fig. 4a. The condensers 9 and lil are substituted therein by condenser-s 9a, 9b and lila, ib, which are permanently adjusted to admit a band of the required width.

It is possible to tune, or vary the center frequency of the frequency scanning panoramic receiver by either adjusting the oscillator condenser I l or by adjusting the center arm of biasing potentiometer '58. This variation can take place either manually or automatically and in the latter case it can be effected by either the same aneroid cell I, which controls the transmitteroscillator, by mechanically linking it to condenser H or by another similarly constructed aneroid cell, as shown in Figs. 4a, llal and 1,5. In Figs. 4 and 4a, I have shown a dotted line between condensers l i and 3 and aneroid cells I, la and ib to show a mechanical link.

This control of the condenser l l by an aneroid cell will afford a constant retuning of the center frequency of the panoramic receiver, this representing at all times the local altitude frequency. The frequencies Aabove and below it represent altitudes above and below it and the bandwidth can be such as to cover an altitude of, for eX- ample, n feet above and n feet below the airplane. The Scale can be expanded or contracted at will. This is useful if the frequency assignment covers a relatively wide band, so as to take care of very great altitudes. The ceiling of modern planes increases continuously and if we would have to cover on a few inches of an oscillograph screen at all times the entire band, the readings may be difficult to make or would not have sufficient accuracy.

With `this method of centering the observation and limiting it by band construction to certain vertical levels above and below the observer, this objection is removed and, besides, the pilot has all the warning and information he wishes, as he is not interested in what happens too high above or too far below him. y

The centering of the local altitude, corresponding to the local altitude-frequency greatly simplifies the design of the commutator controlling this signal. This commutator can be also mechanical as shown in Fig. 4a, acting every time when the receiver tunes through the center region of its band.

In this figure, E05 represents a rotating shaft, which can be that of the motor-generator |55 producing the plate current supply, and which is at ground potential. The plate current of the transmitter from the cathode of the oscillator 'tube S passes through a brush 26| which rides on a metal ring 20mi grounded through the shaft |535. A narrow segment Eiic, of an insulation material periodically interrupts this current, therefore keying off the oscillator tube 6. On the same shaft |05 an insulated ring wild, having a narrow grounded segment lc, and a brush I UI, form the elements controlling .mutators on shaft 65.

phase relationship between the sawtooth voltl age and the keying of the oscillator is determined, one and for all, by the relationship of the brushes I0! and 2M, and of the segments miic and Zeile.

Fig. 3a shows such a time relationship. The upper line represents the sawtooth voitage curve which, in this case, it includes a small time pen riod (t1) representing the current at ground potential as determined by the width of the segment miic. This time period can, however, be

reduced to negligible value by making that segment very thin. The second line represents the variation of plate current in the transmitter showing the time periods when this is oli (t2), this total time period depending upon the width 'of segment 20M. The sharper the circuits of the receiver, the narrower can be made this Segment. By spacing the segments iiic and 25Std, 180 apart, and by maintaining the brushes iii! and 2B! in the same plane, the interruptions f2 will take place atV the moment when the sawtooth current passes through its center value, and therefore when the receiver tunes through its center frequency, or in other words, when lthe stratoscope screen indicates its altitude frequency.

Whereas in Fig. 4, I have shown one aneroid cell I driving the two condensers 3 and Il, in

, Fig. 4a, I show two separate, but identically operating cells, la and ib, each driving one condenser. In the latter figure I also show bandpass input circuits requiring a single adjustment, and a selective auditive response circuit described below.

Frequency seZection.-By connecting headphones or a loudspeaker in the output of the detector, a sound will be heard when a signal appears on any portion of the tuning range. This will, as said before, act as an alarm for the'pilot. It is, however, advantageous, for various purposes, to be able to select for an auditive (or visual) response, only the signals at a given frequency within this range. Such a selective device is shown in Fig. 4a, in which the output of the detector is fed through a push-pull amplifying stage 292m, 2Mb, and a selecting commutator 35a, 35o, 35d, to headphones 34a and/or a neon bulb Mb. This stage 262:1, 292D, operates only periodically when the brush 35a connected to the cathodes of tubes 202er and 2G21) is grounded through the metal segment 35o of the rotary commutator 35d. This commutator is rotated together and in synchronism with the other com- By adjusting the position of the brush 35a around this shaft, by means of a dial, we can select any portion of the bandwidth where the headphones will respond, in other words, any frequency within the range of the receiver. If a signal is present at that frequency a chopped noise is heard. I use a lproperly balanced amplifying stage, in order to Y heard. By setting the brush 35a in a given fixed position, for example corresponding to the ceni ter frequency of the receiver, only signals cordangerous obstacle, fixed or mobile.

i 2 responding to that frequency can be heard. This position may be used permanently and is important for three reasons: l. Because the pilot will receive definite indication of actual danger from an obstacle (plane, for example), situated at his own level. 2. Because it permits means of aural as well as visual signaling for navigational and traffic control, as it will be shown below. 3. Because it permits special uses of ground marker beacons. Such a condition is represented in Fig. 3a in which I show on the lower line the phase relationship between the response of devices Sa, Sb and the sawtooth voltage (which is linked to frequency variation) The solid lines show the last condition described, that is a reponse at the center frequency. The dotted lines on the left of the rst, represent response at a frequency nearer to Fm.

It is possible to link the frequency of one oscillater to the other by many other means, some being electronic, wherein a variation of frequency can be converted, for example, in a variation of voltage and then apply this variation of voltage to the other oscillator to create a variation of frequency again. My receiver is ideally suited for such types of control because I can convert variations of voltage easily into variation of frequencies, through the changing of the bias voltage ll on the reactor tube I5.

In my patents, supra, I have shown how I can simultaneously receive on a frequency scanning panoramic receiver two bands of frequencies which can be observed on two different portions of the oscillograph tube. This is a very important requirement if the receiver is to be used for navigational purposes, so as to avoid carrying on board several receivers. It may be assumed, for example, that the flier wishes to follow a string of radio range beacons and also avoid any The string of beacons may operate on one continuous band of frequencies different Vfrom the altitude frequency band. An electronically controlled receiver showing simultaneously two bands of frequencies can be used advantageously for the purpose. Such results can be obtained in the following manner: synchronously with the sawtcoth generator, I provide means for generating a square-wave alternating-current. This is composed of a series of electrical impulses of a constant amplitude, each such impulse having a duration equal to the duration of one-sawtooth cycle. These impulses are intermittent, each being followed by equal time period 'when no Ycurrent is generated.

Fig. 7 shows on its lower part at M three such square-wave pulsating current impulses; N represents six cycles of synchronous sawtooth cur- 'rent impulses; and M -i-N represents current reby the amplitude of the square-wave input.

At the top of Fig. 7 I show an ordinate representing frequency variation as produced by Vsuch a combination wave in the variable frequency oscillator. It alternately covers the frequencies F1, F2, and Fs, F4. The frequency separation between F2 and F3 can be reduced to zero by reducing the amplitude of the square-wave voltage or be increased to a maximum by increasing that voltage. It can, therefore, be seen that variations of amplitude of M will shift only one band of frequencies (F3 to Fi), and will not aiect the other band. This shift can be 'obtained in the simplest manner by applying the squarewave directly to the biasing potentiometer or resistance 'lll (Figs. 4 and 4a.).

Fig. 5 represents another block diagram showing how this receiver operates. The saine letters are used as 'in Fig. A2 for the common elements `of the two types of receiver transmitter combinations. In Fig. 5 in addition S represents the square-wave generator, and T the mixer of the sawtooth and square-wave currents. Previously to being mixed, the sawtooth component is applied to one of the deecting plates S3 of the cathode ray tube and the square-wave component to another deflecting plate 62, normal to the first, where it is combined with the signal from the channel D.

The effect of this application of the squarewave is to recurrently, and `at the end of each cycle of vthe saw-tooth wave, shift the frequency sweep axis of the cathode ray tube, so as to alternately obtain two parallel lines on which the signals contained in the bands F1 to F2 and, `respectively, F3 to F4 will appear.

The linear separation between these two parallel frequency sweep axes is a function of the amplitude of 'thesduare-wa've voltage applied to 5 the dellecting Aplate 62, and this is controlled through any appropriate means.

Fig. 6 shows a detailed diagram ofthe elements G, S and T of Fig. 5. Tube 8B is a double triode, the grids of which are cross-connected in such `a way that each triode section becomes alternate- `ly blocked. The frequency of this blocking action 'is determined by the rate of charge and discharge oicondenser pairs 8.4, 85, 88 (groups a and b), a pair of which are selected by switch arms V32a and 83h, and also by the value `of the dual rheostats Sia. and 8119.

Another tube 8l acts as a sawtooth oscillator and the frequency controlling elements, that is, condensers 8de, 85o, 86e 'and rheostat Ble, are 'so chosen that they produce a sawtooth current of practically the same frequency as the square- Wave current.

` control the voltage of the deflecting currents put into the vertical and horizontal deflecting plates respectively, of the cathode .ray tube and the amplitude controls 94 and 95 are used to control the voltages applied to the grids of the mixing tube 85 (T in Fig. 5). The-mixed current obtained from the plates of this tube is applied to the frequency controlling tube F.

The lsame results, as `obtained by purely electronic means of tuning, can verywell be obtained `by either purely mechanical or combined electronic and mechanical means such as illustrated in Figs; 8, 9, .11 .and 13. quency modulated oscillator is quite practical and readily made. A `rapidly rotating motor driven condenser produces the frequency shift The mechanically freill `insulating material.

14 required. One' precaution, however, must be taken in avoiding frictional contacts in the tuned circuit, which are invariably noisy, mostly at high frequencies. The best method to avoid this is by using insulated or oating rotors, varying the capacity between two opposite stators. Another precaution which must be taken is to properly balance the rotors dynamically, so as to avoid vibration. This can be obtained by using rotors having several blades, two, three, or more. Such a tWo-bladed rotor is shown at 96a, 9th, in Fig. 8.

The effect of such multi-bladed rotors is to speedup `the number of images for a given motor speed. In ultra-high frequency work, where 'the periodical variation of capacity required is quite small and amounting only to a ew micromicrofarads, I preferto obtain the capacity Variations necessary `by simply rotating a rotor of high dielectric constant between two stator plates connected in the tuned circuit. Several such dielectric rotors can be coupled on one shaft to tune as many circuits as required. One of these rotors can be used for mechanically producing a source of sweep voltage, by the periodical charge and discharge of a condenser, as described in Fig. 4 and in my patents, supra. Fig. 8 is an example of such a construction, in which 96a, Qib represent the two blades of a dielectric rotor having a opening and. rotating between one 'or'two pairs of stator blades 91a, Sl'b and 98a., 98D. We have in fact two distinct variable condensers which can be used in two different circuits or can be connected together for obtaining a larger variable capacitor.

The center of this rotor has a metal bushing ils which is grounded through the shaft H35 of the motor 1126 (Fig. 9) rotating it, and also two small metal sectors lima., ltlb, connecting each of the blades 96a and 96h. A brush lill is riding alternately either over the dielectric or over the grounded metal sectors in such a way as to pass from metal to dielectric exactly at the moment of maximum or minimum capacity of the condenser. This brush periodically discharges condenser 102 to the ground which `condenser becomes charged through a resistor E03 when the brush rides over the dielectric.

Just as in Fig. 4a, the condenser |02 becomes a mechanical source of sweep voltage which is noiseless because the only frictional contact which takes place is to either the dielectric or to a grounded part of the receiver, which is not a part of the tuned circuit.

The electrical connections of such a synchronized dielectric condenser` 'and sweep voltage generator are shown in Fig. 9 in which, for the sake of simplicity; I show only one periodically tuned circuit, an oscillator which can be the element B of the block diagrams. The synchronized condenser and sweep generator replace the elements F and G of those diagrams.

By a slight addition to this construction, I can obtain an alternating coverage of two bands shown on two different lines on the screen of the cathode ray tube, as shown in block diagram, Fig. 5.

On the same shaft m5 of this rotor, I mount a commutator composed of two equal sectors E81 and Hi8, Fig. 10, of double the opening of the blades Sca, 96h, that is 180. One of these sectors `is of metal and grounded to the shaft, and thence to the'chassis; the other sector is of an A brush is@ is connected to a high resistance potentiometer `{Hl-IIL connected on one side to a source of direct current (anode supply for example), and grounded on the other side. This brush will lbe alternately at a certain voltage or at ground potential, as the commutator rotates; a square-wave is mechanically produced, and can serve through condenser -I l2 for shifting the frequency sweep axis on the cathode ray tube as explained before. The same commutator can serve for alternatingly selecting one of two condensers which tune the oscillator circuit, as illustrated in Fig. 1l; it can also serve for mechanically shutting oir or reducing the power of an altitude-indicating ocillator, as illustrated in Fig. 4a. Such a mechanical commutator can be made to open the cathode circuit of the oscillator S for predetermined periods Vof time corresponding to the angle of the commutator sectors. IThe transmitter can be keyed off, for example, alternately during each part of that rotation cycle which produces image of signals on the screen of the receiver.

Mechanical means for producing two band frequency scanning panoramic reception can be better seen in Fig. 11 where, instead of having the condenser H permanently connected in the tuning circuit, I show two condensers Il and H3, each being alternately connected through brushes shown respectively at IM and H39, to the ground.

The different frequency portions are, therefore, alternately covered by the rotating condenser SE-Ql previously described. By individually tuning the condensers Il and l I3, each band may be separately tuned. Condenser I! can, as shown in Figs. 4 and 11, be controlled by a pressure controlled device as an aneroid cell whereas the condenser H3 can be manually controlled for special purposes, as shown hereinafter (Fig. 21).

The block diagram of Fig. 5 can be fully adapted to this arrangement.

The type of mechanical sweep by means of rotating commutators described has one disadvantage; one part of the images is lost by grounding the condenser 132 part of the time. The result of this is more tendency to flicker and less brilliancy of the image as can be seen from Fig. 12. I can, however, advantageously combine electronic tuning and mechanically produced periodical voltage with elimination of this disadvantage, as shown in Figs. la and 13.

In Fig. 13 the condenser m2 has been replaced by a sawtooth oscillator I6 whose grid 89 is synchronized to a mechanical square-wave generator similar to the one heretofore described, but using the 90 sectors lilla, la, |0122, i081).

This form of sector alternately switches in the tuning circuit condensers Vil and H3, at double the rate obtained before. The number of images obtained on the screen is double, because each alternate sawtooth cycle serves to put on the screen one of the frequency bands covered.

Special condensers giving variations of capacity from minimumto maximum over a greater portion of a rotating cycle, however, (270 or more) canrbe used advantageously to reduce the loss-of images mentioned above.

In Fig. 1, I have shown a simple transmitteroscillator whose frequency is controlled by the local atmospheric pressure. I can supplement this information'with that of a direction, which 'may be readily interpreted to indicate a given course, or to directly indicate right and left with respect to said course. Two transmitting antenna have to be used each operating on 'a frequency slightly different from the other, and emitting a directional signal in such an angular relation to each other, as to create an equi-signal path along said course. This method, however, is more completely described in my Patent No. 2,312,203, granted February 23, 1943.Y

Fig. 14 shows such an arrangement in which T1 and T2 are such transmitters, each feeding respectively into the dipoles A1 and A2 at right angles, whereby the courses X1, X2 and Y1, Y2 are created. Supposing now that a 2.5 mc. bandwidth (for example, from 122.5 to 125 mc.) is spread over 2.5 inches of a cathode ray tube screen; this represents a frequency spacing of l megacycle per inch, and a one-eighth inch separation between two signals represents 0.125 mc. If the two signals produced by T1 and T2 are, in other Words, 0.125 mc. apart from each other, they will appear on the screen as two deflections separated by 1/8". If an observer is on the equisignal path, the peaks of the two deflections will appear equally high. If he is on .one side, or the other, one peak, or the other, will predominate. The linear difference between the deflections, corresponding to the amplitude ratio of the two signals, will indicate the number of degrees offcourse.

I have found that it is essential to keep the difference of wave-lengths between these signals as small as possible, so that the number of wavelengths traveled by each signal within a few miles from the station-where the signals are generally more erratic and more subjected to the effects of reflection from obstacles-should be substantially equal, or differing only by .a few wave-lengths. This reduces to a minimum the number of points where falseindications could be obtained if this difference would be greater. This is a fundamental part of my invention distinguishing it from the usual type of dual frequency radio ranges, where no special precautions are taken to maintain this wavelength separation within a minimum value. The frequency scanning panoramic receiver can be made of Vsufcient selectivity to distinguish between two carriers of any frequency separation, asA there are no interfering side-bands such as would be produced by modulating such carriers.

Two signals of very close frequency with their antenna elements quite close to each other are diicult, however, to maintain properly tuned. There is a tendency for these two signals to pull each other in synchronism or to create side-bands by becoming intermodulated.

By proper shielding precautions, it is possible to run the two transmitters together as shown in Fig. 14.

I can avoid, however, completely these diiiculties, by sending signals intermittently through each antenna, in such a manner that when one is on, the other is off. This is represented in Fig. 19, in which T1 and T2 represent the two transmitting circuits including their radiators, emitting signals on adjacent frequencies, and O represents a source which causes these radiators to operate alternately. This switching of the radiators can be obtained either mechanically or electronically. The rst methodl has theadvantage of great simplicity. Y

In all these transmitter arrangements, the frequency or frequencies, can be either fixed or can vary within certain limits as controlled by afrequency controlling element such as an aneroid barometer, as shown in Fig. l. Y v

In the latter case, and` providedl that the aneroid cells used in these transmitters are operating in identical condition', the ground transmitting stations can be used to give absolute altiaaai-eee l? tude indication to the planes in their neighborhood, because both plane receivers and ground transmitters are submitted to similar atmosphericiconditions.

AThe two antennas, whose orientation determines certain courses, can either be fixed or `of variable orientation-.and can be mounted either on a fixed body, or on a mobile body.

In order to extend .the number `of stations which can be used along a given distance, and not to crowd them too much on the screen of a cathode ray tube of relatively small diameter, I prefer in some cases to combine band extension and some manual tuning with frequency scani ning panoramic tuning and, at the same time, use

an indicator showing what part of the band is tuned in. This indicator can be calibrated in units of distance or of altitude, or any other convenient units. Such an arrangement is shown in Fig. 21 in which the screen |4| of a two-band receiver is shown; |02 is a slider which can move to right or left within certain limits by the action of idler pulleys |113, illand manually controlled pulley |45, over which a steel string |56 is wound. This string is connected to the two ends of the slider |42.

This slider can move so that either end of it can come in line with one extremity of the screen of the cathode ray tube. It is calibrated in miles, and their separation corresponds to the separa- .tion between signals appearing on the cathode ray tube screen, for example, as shown in Fig. 2l, when `all the way to the right it will show the `stations from the reference point (Zero miles) up to 200 miles and when all the way to the left itl will show the stations from 200 miles up to 400 miles. This is obtained by connecting the same pulley |45 with the shaft |07 of a rotor of a condenser H3 (see Figs. 11 and 13). A frame in this slider permits insertion of a card showing in their spatial relationship a series of beacon stations, for example from Chicago to Erie. Each beacon station may determine either a two-course or a four-course route, according to the type of antennas they use.

frequency (Fmin) and the slider will, by this Inotion, move to its extreme right position, and the beginning of the dial on the left corresponding to distance Zero, indicating Chicago, will correspond to Fmin on the screen. The dual frequency beacons will apear one after the other, further to the right, as the flier progresses :along the course, several being seen according to their signal strengths. The observer can, if he wishes to, gradually bring them to the center and continuously maintain the true relationship between the reading on the card |48, mileage indication on slider |42 and position oi the signal on screen |4| Such band spreading arrangement as shown is the equivalent of multiplying the diameter of the screen by two. Naturally this can be multiplied still more if desired. As the flier reaches the end of the course marked on the card, he enters a new zone where the frequencies Fmin- Fmax are repeated and he replaces the card |48 with a new one, resetting his dial to Zero miles. By reducing to zero the sweep voltage `applied through potentiometer Z to the reactance tube, such a receiver becomes an ordinary uni-signal receiver tuned at the center frequency defined hereinabove. A switch 205 which has this function is shown in Fig. 4a. The device 34a, Fig. 4a, will then reproduce the auditive .signal of any station which corresponds to that center fre- A flier starting from Chicago will set condenser H3 fully in for lowest A` is Iquency and which can be marked 'as a hairline on the center of the oscillograph screen (Fig 2l) This dial arrangement can very well be used with either a single-band or a two-band frequency scanning panoramic receiver, such as shown in Figs. 5, 6, 7, 11 and 13, in which latter case, one -band is `controlled by a manual setting such as just described (condenser l i3), and the other band by an automatic setting (condenser il) determined, for example, by an aneroid cell, and wherein one setting does not disturb the other one due to the independence of their tuning elements.

Fig. 21 shows such a combination: above the screen 111| an altitude scale'ld'' is used withV the top frequency axis showing 0 in its center. It is calibrated in altitudes up to 2000 feet above to the right, and 2000 feet below to the left of the cen-ter line. An independent, ordinary aitimeter dial M9 may be set nearby, to give the actual altitude which in Fig. 2l is 5200 feet.

A signal |50 appears on the screen, above the line of beacon signals, indicating the presence of a `warning station 'about 1000 feet above the 0bserver, in other words, at 6200 feet. This may be a mountain peak or another plane, and this matter is easily determined, as it will be explained hereinafter, according to the rate of blinking of interruption oi the signal.

In the rst case, the pilot knows that he must rise until the signal passes to the left of the `center line, that-is, below him.

in `the second case, certain trac regulations are applied and as Veach pilot either goes higher or lower, their respective change of position is seen by the two observers in their receivers. Where a receiver such as shown in Fig. 1,1 -is used, the lateral position of the deflections on the lower `frequency axis remain independent of the change in the later position of the deilections on the upper frequency axis because the two frequency bands to which they correspond are independently controlled for the upper and lower line. With reference to Fig. 11 for example, the upper line deflections are controlled by the condenser l1 (which in its turn is controlled by an aneroid cell), and the lower line deflections by condenser ||3 which may be manually controlled. The two functions., however, may be separated if desired and two screens be used, one only for :airway beacons and another for `stratoscope indications.

Fig. 15 ,shows a .single-band stratoscope screen in which the frequency axis is produced vertically. 'Three diierent calibrations appear to the right; the first is of 1.50 feet above and below, -the second is 1500 feet above and below; and the third is 4500 feet above and below. A three-position knob 2Gb is shown below, permitting the selection of any desired band spread. This control is shown on Fig. 4a, as an arm moving ovei` the multitapped resistor 26a. A dual-frequency directional beacon is shown 500 feet below and three obstacles at various altitudes above the observer. The amplitude axis is calibrated in miles corresponding to the strength of stations of equal, standardized power.

Fig. 16 shows the screen of a receiver calibrated in heights from O to 10,000 feet, to be used by the traiiic controlling authorities. It is necessary to either tune this receiver or adjust its altitude scale up or down according to local atmospheric pressure. This tuning or adjustment can be made either manually, or automatically, by means of an Yaneroid cell such as explained above. An ini clined line marked glide path indicates the amplitudes expected from aircraft engaged along s the glide path and their respective distances can be read on the lower scale.

Airway traffic covitoZ.--It is possible to install panoramic receivers for airport traffic control but minus the cathode ray tube, at various points along airways, and to convey the electric impulses creating the deflections of the cathode ray, to a distant point situated at a traffic control center.

These impulses are of two kinds; a periodic voltage which produces the cathode ray sweep and the short impulses created by the signals themselves. There is no need to convey the first type of impulses, because these can be exactly reproduced at the traffic control center. If, for example, a source of 60 cycles alternating current is available, both at the point where the receiver is installed along the airway, and at the control center, an identical sawtooth voltage or any other VVtype of wave having a predetermined shape, can

be produced in both p-laces, in perfect synchronism by known methods. It is possible, however, to use directly the sinusoidal current for the panoramic reception, as it will be shown separately, and in this case the solution is still simpler, because we dispose at both places of the required sweep voltage. The signal impulses can be sent either by wire or by radio communication according to well known methods which do not require description.

The use of sinusoidal currents for sweeping the cathode ray, in combination with another type of wave for the frequency sweep of the oscillator, results in an advantageous spacing of the signals on the screen, which spreads the frequency scale toward the center and compresses it toward the extremities. This 'is a desirable thing in a stratoscope because it is important to be able to read more accurately variations of vertical levels produced nearer the level of the aircraft, rather than at much higher or lower levels. In Fig. 15, I show such a spacing. Furthermore, the use of sine wave simplifies certain construction problems such as, the generation of a special sweep voltage and the difficulties of sending such types of current undistorted over long' lines, for example, from one end to the other of a fuselage. Such sine waves can be used advantageously also for keying or modulating the stratoscope transmitter.

The simplest use of sine wave is to apply it simultaneously to the grid 53 of the reactance tube I5 and to the cathode ray deilecting element 63,' Figs. 4 and 4a. This eliminates also the need of an amplifier tube such as il, as I can obtain the sufficient A. C. voltage directly from a transformer. In order to obtain, however, the desirable non-linear frequency spacing shown in Fig. 15, I must use a wave of pyramid form for the frequency sweep. The simplest way to do this is by using a rotating 180 condenser plate to create the necessary periodical tuning (S5-91, Fig. 11) Such a condenser actually produces a pyramid variation of capacity (or frequency) versus rotation (or time) as shown in Fig. 12.

A motor generator such as |96 producing some A. C. voltage, can be used for supplying both the sine wave required and the motive force for such a condenser variation. Fig. I7 shows the relationship between the various elements. Curve S shows the sine wave producing the cathode ray sweep voltage varying between -l-E and EL Curve C shows the variations of frequency of the frequency scanning panoramic receiver, between Fm and FM passing through a center frequency Fc. These two are in phase to each other, passing through their extreme values at the'same time. As the elements ab and bc on curveS are equal but opposite in direction, and as elements a'b and bc on curve C are also equal and'opposite in direction, the spot on the screen will travel over the same line back and forth, faster in the center and slower nearer the ends of the frequency axis. On this Fig. 17, the curve M shows how the stratoscope transmitter may be modulated with the same sine wave so to obtain the periodical interruption, or modulation, required at the center frequency. rihis line represents a rectified sine wave of the same frequency as S, as shown by the dotted lines showing the original, non-rectifiedcurrent. By supplying such a rectied current to the plate supply of tube t (Fig. 4) marked -i-B, I obtain directly the exact modulation required for rendering the transmitter either completely inoperative, or operative at its lowest plate current, when the frequency scanning panoramic receiver tunes through Fc, the transmitters frequency. This is illustrated in Fig. 17 by the vertical groups of parallel lines passing close to points d, e, f, g, h on curve C. These lines f meet the transmitter plate current curve IVI along a dotted line showing the low current limit where the transmitter stops oscillating. The same results can also be obtained by supplying D. C. plate voltage to +B and using the sine wave for grid modulation, for example, the grid 8S at tube 22. Also, instead of using rectified sine wave, the same results can be obtained by using a sine wave of double frequency of S in the proper phase relationship. The phase shift between sweep frequency and modulating frequency can be obtained by a simple condenser resistance network, and if this is necessary it is preferably used for the sweep voltage, where there is no power required. The condenser plate can, naturally, be mounted so as to remain in phase with that sweep voltage at all times. rEhe capacity variations required for periodically tuning the oscillator, need not take place at or near the oscillator. By using large value capacity, the oscillator coil H5 (Fig. 11) can be tapped down and the lead can be brought to a certain distance.

Station 'identification-The identification of stations may be obtained in various manners with a panoramic receiver, and in ways impossible to be obtained with ordinary receivers.

One of the means which can be used is the rate of interruption of a signal. From the foregoing explanations, it results that either the dual-frequency beacons, or the collision warning signals sent by planes are periodically interrupted or modulated signals. This rate of interruption or modulation can be determined easily, provided that the frequency sweep rate of the frequency scanning panoramic receiver is adjustable. This can be obtained very readily with the electronically controlled sweeps shown and I have provided the necessary controls for this purpose (see {M -8l, Fig. 4). In a mechanically controlled receiver, continuously adjustable speed devices can be used for this purpose, either by varying the speed of the motor itself or of the devices connecting the motor to the receiver.

High frequency sweeps are advantageous when many identifying frequencies are required. In order to be able to use very high frequency sweeps of the order of a few hundred to a few thousand cycles per second, I prefer applying directly to the plate 52 of the cathode ray tube, non-rectified intermediate frequency signals obtained from transformer 41, (Fig. 4). In this case, the de- `such as from motrs or vibrators.

flection's appear on both sides of the frequency sweep axis and take a distinctive appearance frequency of the signal, the signal is picked up at the saine amplitude. If such a signal is interrupted periodically, a perfect synchronism could cause it to be absent in the panoramic receiver entirely. This' can happen in case of collision signals sent by planes, vhich could be synchronized by chance with a receiver, so that they would not vbe received. This, however, would require a combination of coincidental factors, rarely 'met in practice; the two receivers in two different planes would have to be swept in absolute synchronisrn and be tuned to the same frequency continuously. The chance of this condition occurring is remote and is further reduced by reducing the total interruption time of the collision warning transmitter to the shortest possible limit.

The dual-frequency beacons forming part of a common `system can be alternately keyed on and olf at one and the same frequency rate determined by properly adjusting the keying frequency of element O in Fig. 19. The observer can also adjust the sweep frequency of his receiver so as to see, for example, a very slow change of Yoney frequency -to another or he may stop (momentarily land during the identification test) the signal on one frequency only.

By noting the position of the sweep frequency controls at which this occurs, the pilot can distinguish one set of signals from another set. One set of `beacons may have for example, an on-olff rate of 27 cycles per second, another one of 32 cycles per second, and the different settings he would require on his receiver to freeze one set of motions will tell him which set he is considering. This synchronizing is also useful fo-r eliminating certain forms of recurrent noises, The sweep frequency of the receiver can be adjusted in synchron'ism with the source of noise, whereby such noise signals become frozen in a iixed part of the screen where they cause no interference, or may be entirely eliminated.

VDual frequency beacons, therefore, can be made to give characteristic signals which generally appear as two adjacent V-like deflections, closing at the bottom. They cannot be mistaken for ordinary unmodulated signals which are open at `the bottom. Such Vbeacons can be, if desired, code or voice modulated at certain fixed intervals. rThe pilot, having a stratoscope Von board'with a selective auditive device, such as fshown in Fig. en', (35a, c, d, can read such code and identify the station. Phone can be heard on a stratos'cope receiver by simply switching off the frequency sweep and transmitter (switches M5, 2ML-and turning on the switch 203 which outs off the phone chopper. In this case the receiver remains tuned Ato its center frequency, but it' is possible to provide a means to retune temporarily the receiver separately and independently from the `cell lb, by fbias tuning, that is by varying the Vbi'as voltage applied to 4the grid of the reactanc'e tube i5, through the potentiometer Til. In this case, I obtain the equivalent of an ordinary radio receiver, tunable over :a frequency range and permitting two-way communication with Aanother station. The stra-toscope transmitter 6, Fig. 4a, can then be voicemodulated in the usual manner, for example, by the use of a microphone in its cathode circuit (switch 205). It will still be tuned by the aneroid cell, and therefore, continue `to emit collision warn-ings visible on the screens of other receivers.

Aircraft also can be identified, eithel` by the ground observers, cr by pilots of other aircraft, `according to a characteristic rate of modulation which is assigned to each. Such a modulation is produced -by the periodic transmitter modulator 296e, nd, shown in Figs. 4a. By assigning various modulation frequencies `the probabilities of two aircraft operating in absolute synchronism are greatly reduced. By making the 'motor 'SSB rotate at a speed proportional to the air speed of an aircraft, the modulation rate can be used asan indication of speed. Planes flying .in formation can maintain constant speed by maintaining their indications in synchronism.

Further identification can be added by modulating the emitted signals with code or even voice, by simply providing each transmitter with a code wheel or a modulator and a Voice record. 'll-he chopper Edile-2030i itself can be made to have as many inserts Zlc as desired, and the inserts can be of any desired angular size for modulating the transmitter 6 according to CW or as a given tone. A pickup can be put in its cathode circuit which is shown open by switch 2&5.

Two-course beacons are to be preferred to four-course beacons, because they can be made to `give a positive indication of right and left In Fig. 22 I show a course Xi-Xz determined by such a dual-frequency beacon located at 0 and .alternately .emitting on leach side of the course signals L and R on adjacent frequencies FL and FR. Suppose that frequency FL is higher than that of FR, `and a plane carrying a panoramic receiver flies in the direction of the arrow from AX1 to X2. 1f the screen of this receiver is so disposed that higher frequencies are to the left, `and if the plane happens to be on the left side on the line X1-X2, for example, in points Y1 or Y2, the left hand signal becomes taller than the right hand signal (see 22o) and vice versa, if it happens to be on the right side Ys or Y4, the right hand signal becomes taller than the left handsign'al ("see Fig. 22h) Beacons giving, in combination, a number of Vsimultaneous indications can thus be made. As an example, I shall describe one which simultaneously indicates: altitude -of a point, barometric correction, wind direction and velocity. This is simply a combination of the principles `described above. rThe beacon is a dual-frequency two-course radio range transmitter, whose average frequency is determined by a barometer controlled oscillator as nexplained from which he can determine his height above the ground.

The antennas of those two transmitters determine a course similar to Xi-Xz of Fig. 22, but this course is orientable according to wind direction, by pivotingA the antenna array around a central point. Fig. 23 shows in simplified form an upper view of such an antenna array in which 55, |62 are the vertical antennas, each "connected to one transmitter. Each antenna acts as a reflector 'for "the other when one works, 

